A high-entropy doped polyanionic positive electrode material and a preparation method thereof

Abstract

This invention relates to the field of sodium-ion battery materials technology, and discloses a high-entropy doped polyanionic cathode material and its preparation method. It aims to solve the problems of low intrinsic conductivity, poor capacity performance under high compaction density, and easy component segregation in traditional sodium iron pyrophosphate-based cathode materials. The method involves wet mixing of Fe source, at least three M sources, P source, and Na source in deionized water according to the product molar ratio, adjusting the pH to 0-3 to obtain a precursor solution with a total Fe and M ion concentration of 1-4 mol / L. The precursor powder is obtained by spray pyrolysis, then mixed with a carbon source and calcined under an inert atmosphere to obtain the target material. This invention achieves uniform mixing of multiple elements at the atomic scale, optimizes the electronic structure of the material, maintains excellent capacity performance under high compaction density, and significantly improves the volumetric energy density of the battery. Furthermore, the preparation process is short, controllable, and reproducible, showing excellent prospects for industrialization and commercial application.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials technology, specifically to a polyanionic cathode material and its preparation method, particularly a sodium iron pyrophosphate-based cathode material with high entropy doping and high real density characteristics and its spray pyrolysis preparation method. Background Technology

[0002] With the rapid development of large-scale energy storage and low-speed electric vehicles, sodium-ion battery technology, which is abundant in resources and inexpensive, has attracted widespread attention. Among the many sodium-ion battery cathode materials, sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) has become one of the most promising cathode materials due to its stable three-dimensional framework structure, high theoretical capacity (~129mAh / g), environmental friendliness, and good thermal stability.

[0003] However, the practical application of sodium iron pyrophosphate materials faces two key bottlenecks: first, its intrinsic electronic conductivity is relatively low; second, during battery manufacturing, increasing the electrode compaction density to improve volumetric energy density exacerbates interparticle contact resistance and hinders sufficient electrolyte wetting, leading to decreased utilization of active materials and a significant reduction in discharge specific capacity. This phenomenon makes it difficult for the material to maintain its ideal specific capacity during the process of increasing electrode compaction density, limiting its application in scenarios requiring high volumetric energy density.

[0004] Currently, elemental doping is a common strategy for improving the electrochemical performance of materials. However, traditional single or dual-element doping has limited effect on regulating electronic structure, resulting in insufficient performance improvement. In terms of preparation processes, solid-state methods are prone to component segregation and local impurities, while co-precipitation methods have long processes and face significant challenges in controlling the uniformity of multi-element co-precipitation.

[0005] Spray pyrolysis technology, as an advanced process capable of directly obtaining micro- and nano-sized powders from solutions, boasts significant advantages such as short reaction times, high compositional uniformity, and controllable morphology. Combining the "high-entropy" design concept (i.e., introducing three or more metal elements to form a solid solution) with spray pyrolysis technology holds promise for achieving extremely uniform elemental distribution at the atomic scale, synergistically enhancing the electronic conductivity and structural stability of materials, thereby overcoming the performance bottleneck of sodium iron pyrophosphate.

[0006] Developing a novel material system and preparation method that can achieve extreme compositional uniformity and is suitable for high-pressure solid electrode structures has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a high-entropy doped polyanionic cathode material and its preparation method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a polyanionic cathode material includes:

[0010] Step 1: According to the final product Na 4-x Fe 3-y M z The elemental molar ratio of (PO4)2P2O7 is obtained by wet mixing of transition metal Fe source, dopant element M source, P source and Na source in deionized water, adding acid to adjust the pH of the solution to 0-3, and controlling the total concentration of Fe ions and dopant element M ions in the precursor solution to 1-4 mol / L to obtain the precursor solution, wherein 0≤x≤0.1, 0<y≤0.1, 0<z≤0.05, and M is at least three of Ni, Co, Mn, Ca, Mg, Al, Cu, Zn, Mo, V and Cr;

[0011] Step 2: The precursor solution is subjected to spray pyrolysis to obtain spray pyrolysis powder;

[0012] Step 3: Mix the spray pyrolysis powder with a carbon source, grind and dry it, and then calcine it under an inert atmosphere to obtain a high-entropy doped polyanion cathode material.

[0013] In a further technical solution, in step one, the Fe source is selected from at least one of ferrous chloride, ferrous nitrate, ferrous acetate, and ferrous citrate; the P source contains phosphate and / or pyrophosphate, wherein the phosphate is selected from at least one of phosphoric acid, sodium phosphate, and ammonium phosphate, and the pyrophosphate is selected from at least one of pyrophosphate, sodium pyrophosphate, and ferric pyrophosphate; the Na source is selected from at least one of sodium phosphate, sodium pyrophosphate, sodium nitrate, sodium chloride, and sodium acetate.

[0014] In a further technical solution, in step one, the source of the dopant element M is: Ni source selected from at least one of nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate; Co source selected from at least one of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate; Mn source selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; Ca source selected from at least one of calcium chloride, calcium nitrate, and calcium acetate; Mg source selected from at least one of magnesium chloride, magnesium sulfate, magnesium nitrate, and magnesium acetate; Al source selected from at least one of aluminum chloride, aluminum sulfate, aluminum nitrate, and aluminum acetate; Cu source selected from at least one of copper chloride, copper sulfate, copper nitrate, and copper acetate; Zn source selected from at least one of zinc chloride, zinc sulfate, zinc nitrate, and zinc acetate; Mo source selected from at least one of molybdenum chloride, molybdenum sulfate, molybdenum nitrate, and molybdenum acetate; V source selected from at least one of ammonium metavanadate and vanadium oxide; and Cr source selected from at least one of chromium nitrate, chromium oxide, and chromium sulfate.

[0015] In a further technical solution, in step one, the acid solution is selected from at least one of nitric acid, hydrochloric acid, phosphoric acid, oxalic acid, formic acid, acetic acid, propionic acid, citric acid, tartaric acid, malic acid, salicylic acid, and succinic acid.

[0016] In a further technical solution, in step two, the atomization method of the spray pyrolysis is pressure spray, centrifugal spray or ultrasonic spray, and the D50 particle size of the spray pyrolysis droplets is <100μm.

[0017] In a further technical solution, in step two, the spray pyrolysis adopts a three-stage high-temperature pyrolysis furnace, the furnace top temperature is 150-350℃, the furnace in-furnace pyrolysis temperature is 550-750℃, and the furnace bottom temperature is 300-600℃.

[0018] In a further technical solution, in step three, the carbon source is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, lignin, nanocellulose, and phenolic resin.

[0019] In a further technical solution, in step three, the calcination holding temperature is 450-650℃, and the holding time is 5-15h.

[0020] In a further technical solution, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0021] In a further technical solution, in step one, the pH of the acid-controlled solution is 0.5-2.0, and the total concentration of Fe ions and dopant M ions is 2.0-3.0 mol / L; in step two, the D50 particle size of the droplets is 40-70 μm; in step three, the calcination holding temperature is 550-620℃, and the holding time is 6-10 h.

[0022] Furthermore, this invention also discloses a polyanionic cathode material with the chemical formula Na. 4-x Fe 3-y M z (PO4)2P2O7, wherein 0≤x≤0.1, 0<y≤0.1, 0<z≤0.05, and M is at least three of Ni, Co, Mn, Ca, Mg, Al, Cu, Zn, Mo, V, and Cr; the carbon content of the cathode material is 1.0-2.5%, and the compaction density of the electrode sheet prepared from the cathode material is 2.15-2.45 g / cm³. 3 .

[0023] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0024] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0025] This invention innovatively combines high-entropy doping design with spray pyrolysis preparation process, breaking through the technical bottlenecks of low intrinsic conductivity and poor capacity performance under high real density in traditional sodium iron pyrophosphate-based cathode materials. Simultaneously, it optimizes the controllability and industrial applicability of the preparation process, achieving multiple improvements in material performance, preparation process, and commercial applications. Specific technical effects are as follows:

[0026] 1. Significantly optimizes the intrinsic electrochemical performance of the material: By introducing at least three doping elements to construct a high-entropy doping system, the electronic structure of the material is precisely optimized at the atomic scale. This has a significant synergistic effect on improving the intrinsic electronic conductivity of the material and accelerating the diffusion rate of sodium ions. It solves the problem of insufficient conductivity of traditional sodium iron pyrophosphate from the material's essence, and lays a key intrinsic foundation for achieving high capacity under high solid density in subsequent processing.

[0027] 2. Achieving excellent capacity under high compaction density: The precursor prepared by spray pyrolysis possesses highly uniform composition and regular particle morphology, enabling the cathode material prepared by this invention to exhibit excellent high compaction adaptability at 2.15-2.45 g / cm³. 3 Within the high compaction density range, it can still achieve ideal specific capacity, effectively solving the technical problem in the industry that "increasing compaction density easily leads to a decrease in the utilization rate of active materials and a decrease in discharge specific capacity", and significantly improving the volumetric energy density of sodium-ion batteries.

[0028] 3. The preparation process combines controllability and industrialization potential: The core spray pyrolysis technology can directly produce micro-nano-scale powders from the precursor solution in one step. The process flow is short, and it can achieve uniform mixing of multiple elements at the atomic scale. It is also easy to accurately control the morphology of the product. The overall controllability and reproducibility of the process are excellent, providing a reliable process guarantee for the large-scale production of high-entropy doped cathode materials with stable performance, and is suitable for industrial mass production needs.

[0029] 4. Excellent overall material performance and outstanding commercial prospects: The final polyanionic cathode material has a carbon content precisely controlled within a moderate range of 1.0-2.5%, ensuring both conductivity and density. It also achieves a synergistic improvement in high compactness and high capacity. The overall electrochemical performance of the material far exceeds that of similar materials prepared by traditional solid-state methods and other processes. It can be widely adapted to core application scenarios of sodium-ion batteries such as large-scale energy storage and low-speed electric vehicles, and has excellent industrialization and commercial application value. Attached Figure Description

[0030] Appendix Figure 1 This is a SEM image of the spray pyrolysis precursor prepared in Example 1 of the present invention;

[0031] Appendix Figure 2 This is a SEM image of the cathode material prepared in Example 1 of the present invention;

[0032] Appendix Figure 3 The first charge-discharge curve of the coin cell assembled with the positive electrode material prepared in Example 1 of the present invention under 0.1C rate cycling. Detailed Implementation

[0033] The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the embodiments of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0034] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this case.

[0035] The high-entropy doped polyanionic composite sodium iron phosphate cathode material of this invention has the chemical formula Na. 4-x Fe 3-y M z (PO4)2P2O7, where 0≤x≤0.1, 0<y≤0.1, 0<z≤0.05, and M is at least three of Ni, Co, Mn, Ca, Mg, Al, Cu, Zn, Mo, V, and Cr; the carbon content of this material is 1.0-2.5%, and the compaction density of the electrode prepared from it is 2.15-2.45 g / cm³. 3 .

[0036] Unless otherwise specified, all raw materials used in the following embodiments are commercially available analytical grade, and all equipment used is conventional chemical and battery manufacturing equipment; spray pyrolysis is performed in a three-stage high-temperature pyrolysis furnace, and calcination is carried out in an inert atmosphere tube furnace; electrode preparation and battery charge-discharge testing are conventional testing methods in the field of sodium-ion batteries.

[0037] Example 1: The positive electrode material prepared in this example has the chemical formula Na. 4.00 Fe 2.97 Mn 0.01 Ca 0.01 Mg 0.01 The specific preparation steps for (PO4)2P2O7 are as follows:

[0038] 1. Preparation of precursor solution: using Na 4.00 Fe 2.97 Mn 0.01 Ca 0.01 Mg0.01 Using the general chemical formula (PO4)2P2O7 as the stoichiometric standard, ferrous nitrate, manganese nitrate, calcium nitrate, and magnesium nitrate were weighed as metal sources, phosphoric acid and sodium pyrophosphate as phosphorus sources, and sodium nitrate as sodium source. The above raw materials were dissolved together in deionized water, and nitric acid was added to adjust the pH of the solution to 1.0. The mixture was stirred continuously until completely dissolved and mixed, yielding a clear precursor solution with a total concentration of 2.5 mol / L of Fe ions and doped M ions.

[0039] 2. Spray pyrolysis: The above precursor solution is atomized using a pressure atomizer, and the D50 particle size of the atomized droplets is controlled to be about 60μm. The atomized droplets are then passed into a three-stage high-temperature pyrolysis furnace, with the furnace top temperature set at 230℃, the furnace pyrolysis temperature at 650℃, and the furnace bottom temperature at 500℃. The atomized droplets undergo instantaneous drying, thermal decomposition, and preliminary solid-phase reaction in the pyrolysis furnace in sequence, and the spray pyrolysis precursor powder is collected.

[0040] 3. Carbon Coating and Calcination: The above-mentioned spray pyrolysis precursor powder is mixed with glucose, and the amount of glucose added is calculated based on the carbon content of the final product being 1.5%. The mixture is sand-milled until the material is uniformly dispersed. After vacuum drying, the dried powder is placed in a nitrogen protective atmosphere for calcination. The calcination process is as follows: the temperature is raised to 580°C at a heating rate of 3°C / min and held at this temperature for 8 hours. After calcination, the furnace is cooled to room temperature to obtain the high-entropy doped polyanionic composite sodium iron phosphate cathode material of the present invention.

[0041] Example 2: The positive electrode material prepared in this example has the chemical formula Na. 3.99 Fe 2.94 Mn 0.03 Ni 0.01 Mg 0.01 Al 0.01 The specific preparation steps for (PO4)2P2O7 are as follows:

[0042] 1. Preparation of precursor solution: using Na 3.99 Fe 2.94 Mn 0.03 Ni 0.01 Mg 0.01 Al 0.01 Using the general chemical formula (PO4)2P2O7 as the stoichiometric standard, ferrous nitrate, manganese nitrate, nickel nitrate, magnesium nitrate, and aluminum nitrate were weighed as metal sources, phosphoric acid and sodium pyrophosphate as phosphorus sources, and sodium nitrate as sodium source. The above raw materials were dissolved together in deionized water, and nitric acid was added to adjust the pH of the solution to 1.0. The mixture was continuously stirred magnetically until the raw materials were completely dissolved and mixed to obtain a clear precursor solution with a total concentration of 2.0 mol / L of Fe ions and doped M ions.

[0043] 2. Spray pyrolysis: The above precursor solution is atomized using a pressure atomizer, and the D50 particle size of the atomized droplets is controlled to be about 50 μm. The atomized droplets are then passed into a three-stage high-temperature pyrolysis furnace, with the furnace top temperature set at 250°C, the furnace pyrolysis temperature at 700°C, and the furnace bottom temperature at 520°C. The atomized droplets undergo instantaneous drying, thermal decomposition, and preliminary solid-phase reaction in the pyrolysis furnace in sequence, and the spray pyrolysis precursor powder is collected.

[0044] 3. Carbon Coating and Calcination: The above-mentioned spray pyrolysis precursor powder is mixed with glucose, and the amount of glucose added is calculated based on the carbon content of the final product being 1.5%. The mixture is sand-milled until the material is uniformly dispersed. After vacuum drying, the dried powder is placed in a nitrogen protective atmosphere for calcination. The calcination process is as follows: the temperature is raised to 600℃ at a heating rate of 3℃ / min and held at this temperature for 7 hours. After calcination, the furnace is cooled to room temperature to obtain the high-entropy doped polyanionic composite sodium iron phosphate cathode material of the present invention.

[0045] Example 3: The positive electrode material prepared in this example has the chemical formula Na. 4.00 Fe 2.95 Co 0.02 Ni 0.01 Mn 0.02 The specific preparation steps for (PO4)2P2O7 are as follows:

[0046] 1. Preparation of precursor solution: using Na 4.00 Fe 2.95 Co 0.02 Ni 0.01 Mn 0.02 Using the general chemical formula (PO4)2P2O7 as the stoichiometric standard, ferrous acetate, cobalt acetate, nickel acetate, and manganese acetate were weighed as metal sources, pyrophosphate and sodium phosphate as phosphorus sources, and sodium acetate as a sodium source. The above raw materials were dissolved together in deionized water, and citric acid was added to adjust the pH of the solution to 2. The mixture was stirred continuously until completely dissolved and mixed, yielding a clear precursor solution with a total concentration of 1 mol / L of Fe ions and doped M ions.

[0047] 2. Spray pyrolysis: The above precursor solution is atomized using an ultrasonic atomizer, and the D50 particle size of the atomized droplets is controlled to be about 30 μm. The atomized droplets are then passed into a three-stage high-temperature pyrolysis furnace, with the furnace top temperature set at 150°C, the furnace pyrolysis temperature at 550°C, and the furnace bottom temperature at 300°C. The atomized droplets undergo instantaneous drying, thermal decomposition, and preliminary solid-phase reaction in the pyrolysis furnace in sequence, and the spray pyrolysis precursor powder is collected.

[0048] 3. Carbon Coating and Calcination: The above-mentioned spray pyrolysis precursor powder is mixed with sucrose, and the amount of sucrose added is calculated based on the carbon content of the final product being 1.0%. The mixture is sand-milled until the material is uniformly dispersed. After vacuum drying, the dried powder is placed in an argon protective atmosphere for calcination. The calcination process is as follows: the temperature is raised to 510°C at a heating rate of 3°C / min and held at this temperature for 10 hours. After calcination, the furnace is cooled to room temperature to obtain the high-entropy doped polyanionic composite sodium iron phosphate cathode material of the present invention.

[0049] Example 4: The positive electrode material prepared in this example has the chemical formula Na. 3.92 Fe 2.96 Mo 0.01 V 0.01 Cr 0.02 The specific preparation steps for (PO4)2P2O7 are as follows:

[0050] 1. Preparation of precursor solution: using Na 3.92 Fe 2.96 Mo 0.01 V 0.01 Cr 0.02 Using the general chemical formula (PO4)2P2O7 as the stoichiometric standard, ferrous acetate, molybdenum chloride, ammonium metavanadate, and chromium nitrate were weighed as metal sources, ammonium phosphate and sodium pyrophosphate as phosphorus sources, and sodium nitrate as sodium source. The above raw materials were dissolved together in deionized water, and nitric acid was added to adjust the pH of the solution to 1.5. The mixture was stirred continuously until completely dissolved and mixed, yielding a clear precursor solution with a total concentration of Fe ions and doped M ions of 3.0 mol / L.

[0051] 2. Spray pyrolysis: The above precursor solution is atomized using a centrifugal spray atomizer, and the D50 particle size of the atomized droplets is controlled to be about 80 μm. The atomized droplets are then passed into a three-stage high-temperature pyrolysis furnace, with the furnace top temperature set at 280℃, the furnace pyrolysis temperature at 680℃, and the furnace bottom temperature at 450℃. The atomized droplets undergo instantaneous drying, thermal decomposition, and preliminary solid-phase reaction in the pyrolysis furnace in sequence, and the spray pyrolysis precursor powder is collected.

[0052] 3. Carbon Coating and Calcination: The above-mentioned spray pyrolysis precursor powder is mixed with polyethylene glycol, and the amount of polyethylene glycol added is calculated based on the carbon content of the final product being 2.0%. The mixture is sand-milled until the material is uniformly dispersed. After vacuum drying, the dried powder is placed in an argon protective atmosphere for calcination. The calcination process is as follows: the temperature is raised to 550°C at a heating rate of 3°C / min and held at this temperature for 8 hours. After calcination, the furnace is cooled to room temperature to obtain the high-entropy doped polyanionic composite sodium iron phosphate cathode material of the present invention.

[0053] Comparative Example 1: A cathode material with the same stoichiometry as in Example 1 was prepared using a solid-state method. The specific preparation steps are as follows:

[0054] Na according to Example 1 4.00 Fe 2.97 Mn 0.01 Ca 0.01 Mg 0.01 (PO4)2P2O7 stoichiometric ratio: Sodium carbonate, iron phosphate, sodium dihydrogen phosphate, manganese dioxide, calcium oxide, and magnesium oxide were weighed and dispersed in deionized water. Glucose with a carbon content of 1.5% corresponding to the final product was added. The mixture was milled until uniformly dispersed. The milled slurry was vacuum dried, and the dried powder was calcined under a nitrogen protective atmosphere. The calcination process was as follows: the temperature was increased to 580℃ at a rate of 3℃ / min and held at this temperature for 8 hours. After calcination, the furnace was cooled to room temperature to obtain the doped sodium iron phosphate cathode material prepared by the solid-state method.

[0055] Comparative Example 2: Comparative Example of Single Element Doping (Mn Single Doping): The cathode material prepared in this comparative example has the chemical formula Na. 4.00 Fe 2.97 Mn 0.03 The preparation steps for (PO4)2P2O7 are exactly the same as those in Example 1, except that the doping element is changed to a single Mn element, while the other process parameters, raw material types and amounts remain unchanged.

[0056] Comparative Example 3: Comparative Example of Dual-Element Doping (Mn, Ca Dual Doping): The cathode material prepared in this comparative example has the chemical formula Na. 4.00 Fe 2.97 Mn 0.02 Ca 0.01 The preparation steps for (PO4)2P2O7 are exactly the same as those in Example 1, except that the doping elements are changed to Mn and Ca. All other process parameters, raw material types and amounts remain unchanged.

[0057] Performance testing and results analysis:

[0058] The positive electrode material, conductive agent, and PVDF binder obtained in Examples 1-4 and Comparative Example 1 were mixed at a mass ratio of 94:3:3 to prepare an electrode slurry, which was uniformly coated onto an aluminum foil current collector. After drying and rolling, a positive electrode sheet was formed. A sodium metal sheet was used as the counter electrode, glass fiber as the separator, and an ether electrolyte as the electrolyte. CR2032 coin cells were assembled in an argon-protected glove box. The charge / discharge test voltage window of the battery was 2.0~3.6V, the test environment temperature was 25℃, and a constant current charge / discharge test was conducted using a current density of 0.1C (1C=129mAh / g). Key performance data are summarized in Table 1 below:

[0059] Table 1 Performance of cathode materials

[0060]

[0061] As shown in the test data in Table 1 above, the high-entropy doped polyanionic composite sodium iron phosphate cathode materials prepared in Examples 1-4 of this invention have an electrode compaction density of 2.37-2.41 g / cm³. 3 Compared with Comparative Example 1 (2.15 g / cm³), 3 Increased by approximately 0.22-0.26 g / cm³ 3 The 0.1C discharge specific capacity reaches 111.5-113.1 mAh / g, an improvement of 4-9 mAh / g compared to comparative examples 1-3 (104.2-108.9 mAh / g); the first-cycle efficiency reaches 94.2%-94.6%, both higher than the comparative examples; the capacity retention rate after 500 cycles at 1C reaches 97.9%-99.2%, far exceeding that of comparative examples 1-3 (93.6%-96.2%). These results fully demonstrate that this invention, through the synergistic effect of high-entropy doping design and spray pyrolysis process, successfully solves the industry problem of insufficient capacity utilization under high high-density conditions in traditional sodium iron phosphate cathode materials, achieving a synergistic improvement in both high high-density and high electrochemical capacity, and significantly enhancing the volumetric energy density of sodium-ion batteries.

[0062] like Figure 3 As shown, the first charge-discharge curve of the coin cell assembled with the cathode material prepared in Example 1 of the present invention is shown at a 0.1C rate. The blue curve in the figure is the discharge curve, and the orange curve is the charging curve.

[0063] In summary, this invention constructs a high-entropy system by introducing at least three doping elements, optimizes the electronic structure of the material at the atomic scale, effectively improves its intrinsic electronic conductivity and sodium ion diffusion rate, and lays the intrinsic foundation for improving material performance.

[0064] like Figure 1 The image shows the precursor obtained from spray pyrolysis. Figure 2 As shown, the cathode material exhibits a regular spherical morphology after calcination. Spherical particles facilitate good particle rearrangement and electrolyte wetting under high compaction density, thus ensuring high capacity performance of the material under high compaction conditions and significantly improving the volumetric energy density of sodium-ion batteries.

[0065] The preparation process of this invention is short and highly controllable, facilitating the uniform mixing of multiple elements and precise control of product morphology. It exhibits excellent process reproducibility and promising prospects for industrial application. The resulting cathode material maintains a moderate carbon content of 1.0-2.5% while achieving a synergistic improvement in both high compaction density and high capacity, demonstrating excellent comprehensive electrochemical performance and commercial application value.

[0066] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy doped polyanionic cathode material, characterized in that: include: Step 1: According to the final product Na 4-x Fe 3-y M z The elemental molar ratio of (PO4)2P2O7 is obtained by wet mixing of transition metal Fe source, dopant element M source, P source and Na source in deionized water, adding acid to adjust the pH of the solution to 0-3, and controlling the total concentration of Fe ions and dopant element M ions in the precursor solution to 1-4 mol / L to obtain the precursor solution, wherein 0≤x≤0.1, 0<y≤0.1, 0<z≤0.05, and M is at least three of Ni, Co, Mn, Ca, Mg, Al, Cu, Zn, Mo, V and Cr; Step 2: The precursor solution is subjected to spray pyrolysis to obtain spray pyrolysis powder; Step 3: Mix the spray pyrolysis powder with a carbon source, grind and dry it, and then calcine it under an inert atmosphere to obtain a high-entropy doped polyanion cathode material.

2. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step one, the Fe source is selected from at least one of ferrous chloride, ferrous nitrate, ferrous acetate, and ferrous citrate; the P source contains phosphate and / or pyrophosphate, wherein the phosphate is selected from at least one of phosphoric acid, sodium phosphate, and ammonium phosphate, and the pyrophosphate is selected from at least one of pyrophosphate, sodium pyrophosphate, and ferric pyrophosphate; and the Na source is selected from at least one of sodium phosphate, sodium pyrophosphate, sodium nitrate, sodium chloride, and sodium acetate.

3. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step one, the source of the dopant element M is: Ni source is selected from at least one of nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate; Co source is selected from at least one of cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate; Mn source is selected from at least one of manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate; Ca source is selected from at least one of calcium chloride, calcium nitrate, and calcium acetate; Mg source is selected from at least one of magnesium chloride, magnesium sulfate, magnesium nitrate, and magnesium acetate; Al source is selected from at least one of aluminum chloride, aluminum sulfate, aluminum nitrate, and aluminum acetate; Cu source is selected from at least one of copper chloride, copper sulfate, copper nitrate, and copper acetate; Zn source is selected from at least one of zinc chloride, zinc sulfate, zinc nitrate, and zinc acetate; Mo source is selected from at least one of molybdenum chloride, molybdenum sulfate, molybdenum nitrate, and molybdenum acetate; V source is selected from at least one of ammonium metavanadate and vanadium oxide; and Cr source is selected from at least one of chromium nitrate, chromium oxide, and chromium sulfate.

4. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step one, the acid solution is selected from at least one of nitric acid, hydrochloric acid, phosphoric acid, oxalic acid, formic acid, acetic acid, propionic acid, citric acid, tartaric acid, malic acid, salicylic acid, and succinic acid.

5. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step two, the atomization method of the spray pyrolysis is pressure spray, centrifugal spray or ultrasonic spray, and the droplet D50 particle size of the spray pyrolysis is <100μm.

6. The method for preparing a high-entropy doped polyanionic cathode material according to claim 5, characterized in that: In step two, the spray pyrolysis adopts a three-stage high-temperature pyrolysis furnace. The furnace top temperature is 150-350℃, the furnace in-furnace pyrolysis temperature is 550-750℃, and the furnace bottom temperature is 300-600℃.

7. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step three, the carbon source is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, lignin, nanocellulose, and phenolic resin.

8. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step three, the calcination temperature is 450-650℃ and the holding time is 5-15h.

9. The method for preparing a high-entropy doped polyanionic cathode material according to claim 1, characterized in that: In step one, the pH of the acid-controlled solution is 0.5-2.0, and the total concentration of Fe ions and dopant M ions is 2.0-3.0 mol / L; in step two, the D50 particle size of the droplets is 40-70 μm; in step three, the calcination holding temperature is 550-620℃, and the holding time is 6-10 h.

10. A high-entropy doped polyanion cathode material, characterized in that: The positive electrode material is prepared by the preparation method according to any one of claims 1 to 9, wherein the chemical formula of the positive electrode material is Na. 4-x Fe 3-y M z (PO4)2P2O7, wherein 0≤x≤0.1, 0<y≤0.1, 0<z≤0.05, and M is at least three of Ni, Co, Mn, Ca, Mg, Al, Cu, Zn, Mo, V, and Cr; the carbon content of the cathode material is 1.0-2.5%, and the compaction density of the electrode sheet prepared from the cathode material is 2.15-2.45 g / cm³. 3 .

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